1. Field of the Invention
The present invention relates to a multilayered-eddy-current type strong magnetic field generator which is suitable for various research works in magnetics engineering such as studies of magnetic properties of materials, in power magnetics, in bio-magnetics, and in nuclear fusion. More particularly, the invention relates to a strong magnetic field generator which can continuously generates an extremely strong magnetic field by superposing multiphase eddy currents which are individually induced in multiple conductor layers respectively.
2. Related Art Statement
Much efforts are currently undertaken for research and development of strong magnetic field generators by using large-scale experimental facilities, in order to promote investigations and studies of properties of materials in strong magnetic field, preparation and testing of new materials and experiments on nuclear fusion.
Conventional strong magnetic field generators can be classified into several groups; namely, destructive pulse strong magnetic field generators such as those of KNER method and the implosion method, non-destructive pulse strong magnetic field generators such as those of the multilayered coil type and the so-called MIT type, and continuous strong magnetic field generators such as those of superconductive type and hybrid type.
The strong magnetic field generators of the prior art provided very strong magnetic fields. However, these generators have shortcomings in that the duration of the strong magnetic fields generated is very short, that special facilities such as extremely low temperature apparatus and large power source apparatus are required, that only pulse or direct-current (DC) magnetic field can be generated and that continuous generation of strong alternating-current (AC) magnetic field is not possible.
In order to overcome the above shortcomings of the prior art and to facilitate continuous generation of strong AC magnetic field, the inventors proposed an eddy current type strong AC magnetic field generator in their Japanese Patent Application No. 61(1986)-228,459. More specifically, the eddy current type AC magnetic field generator which was previously proposed by the inventors uses a conductor plate placed in an AC magnetic field to be produced by an electromagnet formed of a coil, so that an eddy current is induced in the conductor plate for generating a counter magnetic field for neutralizing the AC magnetic field of the electromagnet. A cavity is bored in the conductor plate in such a manner that the AC magnetic field due to the eddy current is converged in the cavity so as to intensify the magnetic flux density to an extremely high level at the cavity. Thereby, a very strong AC magnetic field is generated at the cavity by converging the eddy current thereat.
However, the above proposed eddy-current type strong AC magnetic field generator is constructed such as a pair of coils are disposed respectively on both sides of two conductor plates forming a narrow slit therebetween or a single conductor circular plate having a narrow radial slit extending from a periphery to a central hole thereof. Thus, the above eddy-current type strong AC magnetic field generator has a defect that the leakage of magnetic flux to be converged is fairly large, so that it has been difficult to intensify the density of AC magnetic flux in the slit or the central hole to a theoretically expected level.
Subsequently, the inventors disclosed a multilayered-eddy-current type strong magnetic field generator based on the improvement of the above proposed generator in Japanese Patent Application No. 62(1987)-62,708 specification. The above disclosed strong magnetic field generator, which is provided for efficiently increasing the density of AC magnetic flux on the basis of the magnetic flux leakage reduction effected by converging the eddy current generated in the conductor body surrounded by the exciting coil around the central hole of the conductor body, is arranged as shown in FIG. 5. In this arrangement, respectively multilayered conductor cylinders 5.sub.-1a to 5.sub.-3a and 5.sub.-1b to 5.sub.-3b and exciting coils 10a to 12a and 10b to 12b, which are symmetrically disposed in concentric state on upper and lower sides of a circular conductor plate 4, are alternately combined with each other and eddy currents generated in each of the concentric conductor cylinders are converged around a hole 3 provided at the center of the circular conductor plate 4 along a slit 2, so as to efficiently converge magnetic fluxes in the central hole 3.
However, in the conventional multilayered-eddy-current type strong magnetic field generator as disclosed in FIG. 5, the exciting coils 10a,b to 12a,b are concentrically disposed around the central hole 3, so that respective impedances of these exciting coils are different from each other in order and hence respective eddy currents excited around the central hole 3 by respective coils are different from each other in order. As a result, it is a difficulty of the conventional strong magnetic field generator of this type that the balanced excitation effected multiphase AC currents is hardly available.